The present invention relates to a preparation method of a YBa.sub.2 Cu.sub.3 O.sub.x superconductor, wherein x=7 -.delta., having high transport critical current (Ic) and critical current density (Jc), obtained by a modified melt-textured growth method. In accordance with the present invention, the YBa.sub.2 Cu.sub.3 O.sub.x superconductor formed possesses high transport Ic and Jc.
The discovery of high critical temperature superconducting oxides, including a number of materials which superconduct above liquid-nitrogen temperature, has stimulated considerable interest and activity. A limit to applications of these materials is the low critical current density Jc measured in bulk polycrystalline samples. Several fabrication techniques to increase transport Jc have been reported in the conventional literature. Magnetic field alignment, melt-textured growth, and liquid phase methods can significantly enhance Jc values. Currently, further fabrication techniques for the preparation of YBa.sub.2 Cu.sub.3 O.sub.x superconductors and the products thereof have been proposed. However, if these superconductors are to be practically useful, the transport critical current density should be greater than 10,000 A/cm.sup.2 at liquid nitrogen temperature (77K). These YBa.sub.2 Cu.sub.3 O.sub.x superconductors obtained from general methods possess a transport critical current density from 150 to 600 A/cm.sup.2 at 77 K. However, these values are far below the applicable range. The transport critical current density of a single crystal may be greater than 10.sup.4 A/cm.sup.2, but the size of the product is small, which cannot be used in practice. The transport critical current density of epitaxially grown thin films may be greater than 10.sup.6 A/cm.sup.2, but the film is thin, and the critical current (Ic) can only reach a maximum of about 3 to 5 amp (A). Besides, the thin film must be deposited onto an expensive single crystal substrate. Thus, the application of the product obtained in accordance with the prior process is not so convenient.